AbstractPurpose The overall aim of this study was to clarify and better characterize the sleep/circadian patterns of adolescents in a nationally representative sample. Methods We used three waves of data from the National Longitudinal Study of Adolescent Health to assess sleep/circadian patterns of 2,700 adolescents in grades seven through 12. Results Late school year bedtime was associated with shorter total sleep time cross-sectionally, whereas late summertime bedtime was not. Moreover, late school year bedtime was not associated with late summertime bedtime cross-sectionally. Late school year bedtime in Wave I (1994–1995) was associated with worse educational outcomes and emotional distress 6–8 years later. In addition, late summertime bedtime in Wave II (1996) was associated with more emotional distress at Wave III (2001–2002). Short total sleep time was not associated longitudinally with changes in emotional and academic functioning. Across Waves I and II, more than three quarters of adolescents who went to sleep at 11:15 a.m. or later during the school year or 1:30 a.m. or later during the summer reported sleeping fewer than the recommended 9 hours. Conclusions These findings underscore the significance of evaluating and monitoring bedtime in adolescents and the importance of intervention strategies that target bedtimes in an effort to reduce associated functional impairments, and improve academic and emotional outcomes.